1. Field of the Invention
The invention relates in general to the power supply control for a computer system and, in particular, to the security control of the supply of power to a computer system. More particularly, the invention relates to the effective security control of the supply of power to a computer system for restricting unauthorized access to the system and for avoiding possible damage to the system as a result of repeated trial access by powering up the system.
2. Technical Background
In typical microprocessor-based personal computer or workstation systems, simple mechanical on/off contact switches were used to implement the supply or cut-off of electrical power to the power supply unit of early designs of these computer systems. When the mechanical contact switch installed in the power supply unit of a computer system is turned off, open circuit status of the switch terminates the supply of electrical power to the power supply circuitry, and the entire computer system is turned off. On the other hand, when the same main switch is turned on, the close-circuited switch supplies electrical power such as the house 110V AC to the power supply circuitry, which converts the AC power into the appropriate DC powers (such as, positive and negative 5 and 12 volts DC) for supplying to all the subsystems in the computer. With the steady supply of all the necessary DC powers, the computer system may then initiate its start-up sequence, and the system boots up subsequently.
Mechanical contact switches used in these earlier computer systems relies on human operation by hand, so that the computer system can be turned on or off. Without the intervention of human operator, the computer had no means to turn itself power-on or -off. Meanwhile, once the main power switch is switched and maintained on, the system would initiate and execute its starting sequence of operations. If no effective password control scheme was incorporated at either the system firmware (that is, the Basic Input/Output System (BIOS) in the case of a .times.86-based IBM-compatible computer) or the operating system level, once powered up, the entire system, together with all its data, is exposed to anyone having access to the system.
Models of the Macintosh series of personal computer systems manufactured by Apple Computer Inc. of Cupertino, Calif. employ a designated key on the keyboard to control the powering up and down. Though convenient, however, they also lack the effective security as in the early IBM-compatibles. Once a system has its power cord connected in the utility socket, anyone who can get access to the computer can simply bring up the system by depressing the power up key on the keyboard. Such "soft power control" is open to anyone having access to the keyboard of the system. Firmware and/or operating system level program routines similar to those mentioned above in the .times.86 world would have to be used to provide access restriction for these computer systems.
On the other hand, Intel Corporation of Santa Clara, Calif. had proposed a computer motherboard specification known as the ATX standard whose power supply subsystem no longer relies on the simple mechanical contact switch for the direct power up and down control of the computer system. Instead, the ATX implements a form of soft power control under supervision of a circuitry integrated in the computer system itself. Functionality more than simply and manually switching on and off on the main power switch are provided to a motherboard of the ATX standard so that control over the computer system can be more versatile.
For example, in the case of ATX specification version 2.01, the standby power 5VSB is a 5-volt DC power source that fans out a maximum of 0.7 amperes of current. This provides power for those basic power management circuitry in the computer system when the main power supply is cut off. These power management circuitry may be programmed to implement various convenience functionality of the computer system. For instance, the system can be programmed to start itself automatically in the midnight in a manner unattended by any operator so as to send international facsimile transmissions in the discount rate time periods of the local telephone company. Or, the computer system may be waken up in the evening by the incoming requests for remote modem connection in order to receive file transmissions.
However, such concepts of soft power management as implemented by these recent standards such as ATX still lack the provision for positive data protection by proper security measures as did the above-described prior-art computer systems. When a computer system adopting the ATX standard is started by a user (either authorized or not) by switching-on the main power switch, the power supply is then turned on, and the system initiates to perform its start up sequence of operations. At this moment, if neither the system firmware nor the operation system has been equipped with adequate security program such as password checking, anyone has direct access to the system can have access to the data contained in the computer. Such systems are as unprotected as were the earlier generation of computers having mechanical main power switch.
When such a conventional computer system equipped with a firmware or operating system-level security system is subject to unauthorized access, whoever trying to break into the system must enter the correct password. However, most conventional computer systems employ a simple rule of password entry, namely, the user can try a limited number of times to enter the password. If after the specified times of trial, the unauthorized user still could not enter the correct password, the system would simply lock. Keyboard of the computer system will no longer be responding to any new entries. In this case, the unauthorized user will have to turn off the power to the computer system and then turn it back on again. This allows the unauthorized user to get to the new password entry-point again. This process of power-on and -off must be performed repeatedly before the correct password is entered if the unauthorized user wished to keep trying to break into the system. During this process of repeated switching-on and -off of the main power supply, the computer system is exposed to increased possibilities of premature failure. This is because a normal computer system has not been designed to operate this way.
As is familiar to experienced ones in the field, microprocessor-based computer systems operate on power supply subsystems that do not allow for, at least do not recommend, repeated switching-on and -off during a short period of time. Successive power-on and -off actions within a short period of time are considered un-normal operation though they are basically allowable for well-designed power supply units. These power supplies are equipped with protection circuitry that prevents themselves from powering-on within a specified time period of, for example, a few seconds after being turned off. Though circuit boards in a computer system can thus be protected from potential damages in successive power-on and -off sessions when a unauthorized user tries to break into the system, other components such as disk drives are not as well protected. This is because spindle motors for modem hard disk drives are not designed for such operation schemes. They are supposed to be turned on and maintained power-on for a long period of time.